1. Technical Field
The present disclosure generally relates to spinal surgery, and more particularly, to a device and method for distracting and maintaining the distracted position of adjacent vertebral bodies during a surgical procedure within a vertebral disc space.
2. Background of the Related Art
The structures of the spine include vertebral bodies, vertebral discs, ancillary ligaments and facet joints. The vertebral discs are cushion-like separators between the vertebrae that permit movement of the spine. Each normal human vertebral disc is made up of an outer circumferential ring of laminated fibers made of an elastic hydrogel material. This ring is known as the anulus and has a thickness ranging between 5-15 mm. The anulus surrounds a nucleus center of the vertebral disc which also contains the hydrogel material. Together, the anulus and nucleus of the vertebral disc as well as the bony end plates of adjacent vertebrae bear about 80% of the combined forces of body weight and muscular contractions of the human body. The remaining 20% of combined forces are borne upon the facet joints and other vertebral structures.
The concentric layers of the anulus are primarily made up of collagen fibers which are remarkably tough, resilient and quite flexible but are almost completely inelastic. The human anulus includes these concentric layers or plies with the fibers of the layers positioned in random patches. If the hydrogel located at the center of the nucleus is diminished by age, damage or disease, the fibers of the anulus become lax and the vertebral disc may bulge abnormally. With extreme bulging there may rapidly develop torsional instability in the vertebral discs resulting in a coming apart or de-lamination of the plies of anulus fibers. In many patients, this cascade of disc degeneration results in segmental pain. On the other hand, if the nucleus remains well hydrated and only patches of the anulus fiber layers becomes weakened or torn by an accident, a loose radiating channel may develop through adjacent patches and provide an escape route for portions of the high-pressure hydrogel of the nucleus. This escape of tissue and byproducts outside the anulus is generally known as a herniated disc.
The escape or leaking of byproducts produced by the nucleus through an anulus defect may reach nerve endings found in the outer layers of the vertebral disc and cause severe back pain. If the escape of the byproducts reaches a large spinal nerve, the spinal nerve may become damaged and leg pain may follow. In about 15% of patients having spinal segmental degeneration, the leaking does not heal and the pain becomes chronic and disabling with surgery being required to alleviate the pain. Surgery known as vertebral fusions are the most commonly used surgical techniques used to successfully treat this type of spinal problem.
Vertebral fusions alleviate back pain primarily by stopping all motion of the involved spinal segments. Vertebral fusion operations are performed in some 150,000 U.S. patients annually with a fusion rate approaching 95% and a significant clinical improvement in about 85% of the cases. The need for improved, safe, effective, simpler and less invasive fusion techniques and devices continues to grow. A preferred method of fusion is to insert a bone, bone substitute, prothesis or a device containing bone into a surgically prepared vertebral disc space. The preparation for the bone or device insertion requires that the disc space be forced open and maintained open while the vertebral disc nucleus is removed. Several types of vertebral disc space distraction or spreading devices have been developed for this purpose.
While the disc space is maintained open by a distraction instrument, the surgeon works deeply within the space to remove dead or herniated tissue or bone spurs and then excises portions of the end plates of the vertebrae. Such continuous distraction can be accomplished by several techniques and apparatuses. The prosthesis or bone insert to be implanted can itself be wedge shaped and driven into the vertebral disc space which creates its own distraction of the vertebral bodies. However, the potential for expulsion of the inserted protheses or bone insert has proved too great and the striking force needed to seat the insert into the vertebral disc space has often fractured the vertebral bodies. Further, the deep dissection of the vertebral disc space has to be performed before driving the insert into its final position, but since distraction is needed while the dissection takes place, therein lies a mutually conflicting situation.
Recently vertebral fusion devices having threaded, hollow cages with a tapered outer shell have been used to separate the vertebral bodies. However, the placement of any insert by definition obstructs the passage to deeper tissues of the vertebral space. It has become clear that in preparation for most implants, the distracting force is best applied at a distance from the disc space or at locations within the vertebral disc space that are away from the dissection and the subsequent implantation of the insert.
The most common instruments used to apply distracting force between adjacent vertebral bodies attach directly to the vertebral bodies and neural arches or are placed inside the disc space off to a side between adjacent end plates of the vertebral bodies. The direct vertebral attachment devices utilize pins or screws driven into the vertebral bodies and are attached to a spreading apparatus which forces open the disc space. However, since the pins or screws are usually several centimeters in length, they can also obstruct the surgeon""s vision and/or working space. The least obtrusive direct spreading devices utilize very low profile screws and a method to fasten a spreading member onto the screws. Nonetheless, these devices usually employ a long handled pliers-like appliance to engage the screws and remain attached to them throughout the operation. A typical device used to spread the neural arches and therefore the associated vertebral disc space of adjacent vertebrae is a lamina spreader. Such a device has opposing members that hook into the laminas that lie above and below the disc space. These hooks are forced apart by an attached rack and pinion mechanism or by a hinged appliance having a ratchet lock. Similarly, intradiscal spreaders apply force directly via blade members to the end plates of the vertebrae in order to spread them apart. Since the distraction portions must be unobtrusive to the surgeon, they must be small and placed laterally out of the way. The small footprints of the blade members often cut into the vertebral bone which can create an undesirable situation. The distraction may even fail as the blade members sink into the end plates or crack the vertebrae.
Nevertheless, all of these distraction devices present obstructions to the open surgical field and are often a substantial nuisance to the surgeon. The need for a small, unencumbering, low profile, easily applied distraction has been needed, especially when used in conjunction with the instrumentation for threaded fusion cages. The device of the present disclosure accomplishes these goals and permits important improvements in the intraoperative distraction of the vertebral disc space.
The present disclosure is directed to a distraction device and method of use for distracting and maintaining the distracted position of adjacent vertebral bodies during a surgical procedure within a vertebral disc space. The distraction device of the present disclosure is preferably used on surgical procedures involving vertebral disc space dissection and intervertebral fusion implants.
Accordingly, the distraction device preferably includes a first and second plate, each of which include at least one extension member for removably attaching to a vertebral body, and a locking member for locking the first plate with respect to the second plate across a vertebral disc space. Each extension member includes at least one bore for receiving a bone screw. The distraction device further includes a cam mechanism for relative movement between the first and second plates. The first plate and second plates are preferably crescent shaped and are coupled together by a pin member. The first and second plates are rigidly locked together in a distracted position by a threaded locking screw.
A method of distracting a space between vertebral body portions is also disclosed. The method includes the step of mounting a distraction device to vertebral body portions to access the vertebral space therebetween. The distraction device includes a first and second plate, each of which have at least one extension member for removably attaching to the vertebral body portions, and a locking member for locking the first plate with respect to the second plate across the vertebral space. Other steps include distracting the vertebral body portions to a distracted position with respect to the vertebral space and locking the locking member of the distraction device to rigidly secure the vertebral body portions in the distracted position.
Preferably, the step of distracting a space between vertebral body portions further includes rotating the cam mechanism and inserting a guide between the vertebral body portions and the step of locking further includes rotating a locking screw.
In an alternative embodiment, a method of using a distraction device during implantation of a fusion implant is disclosed. The distraction device is mounted to vertebral body portions to access the vertebral space therebetween and includes a first and second plate, each of which have at least one extension member for removably attaching to the vertebral body portions, and a locking member for locking the first plate with respect to the second plate. A guide is inserted between the first and second plates of the distraction device for distracting the vertebral body portions to a distracted position with respect to the vertebral space. The locking member of the distraction device is locked to maintain the vertebral body portions in the distracted position. Other steps include dissecting at least a partial area of the vertebral space for insertion of a vertebral implant and inserting the vertebral implant within the dissected area of the vertebral space.
Preferably, the step of dissecting further includes removing the guide from within the first and second plates for access to the vertebral space and the step of inserting further includes inserting a fusion cage within the dissected area of the vertebral space.